Spark plug center electrode to insulator connection



Oct. 28, 1958 E A. CANDELISE SPARK PLUG CENTER ELECTRODE TO INSULM'ORCONNECTION Filed June 11, 1956 .wkgoa/ i 5 a 2 0 H! i yway $22256 UnitedStates Patent SPARK PLUG CENTER ELECTRODE TO INSULATOR CONNECTION AlfredCandelise, Flint, Mich., assignor to General Motors Corporation,Detroit, Mich., a corporation of Delaware Application June 11, 1956,Serial No. 590,564

2 Claims. (Cl. 174-152) This invention relates to an improvedself-locking threaded element particularly advantageous in combinationas an electrical contact for spark plugs and the like.

One object of the invention is the provision of an improved self-lockingthreaded element.

Another object is the provision of an improved electrical contact forspark plugs and the like which is of low cost construction and which maybe simply and economically assembled into the spark plug therebyfacilitating production operations.

More particularly, it is an object of the invention to provide animproved spark plug incorporating a threaded electrical contact elementfor the centerwire which may be easily assembled to the spark plug butwhich, once assembled, is locked against removal therefrom.

Other objects and advantages of the invention will appear more clearlyfrom the following description of a preferred embodiment and from theaccompanying drawings thereof in which:

Figure l is a side view in partial section of an aircraft type sparkplug incorporating the invention;

Figure 2 is an enlarged view of the electrical contact element shown inFigure 1;

Figure 3 is a section on the line 33 of Figure 2; and

Figure 4 is a view similar to Figure 3 but showing the contact elementprior to assembly within the spark plug.

Referring now to Figure 1, there is shown an aircraft spark plugincluding metal shell 4 and ceramic insulator 6 having centerbore 8through which there extends an electrical conducting path, generallyreferred to as the centerwire, including as separate but electricallyconnected elements a center electrode spindle 10 which is sealed withinthe insulator and which terminates in a firing tip, resistor cartridge12, externally threaded hollow electrical contact cap 14, and contactspring 16 which extends into the hollow contact cap through the open endthereof and is biased between the resistor cartridge and the contactcap. To accommodate assemblyof the contact cap 14, a portion of theinsulator centerbore is of enlarged diameter and threaded as shown at18.

In accordance with the present invention, a portion of the externalthread on the contact cap is formed by a section or loop of wire 20 oneend of which is secured to the contact cap as by the weld shown at 21.It is desirable that the portion of the thread formed by the wire 20 beintermediate the ends and adjacent the middle of the threaded portionand that the wire 20 be of such length as to form slightly less than oneturn of the thread. In the preferred embodiment shown, the thread hasthree complete turns, the middle one of which comprises the wire 20which is of such length as to form approximately but just less than onecomplete turn. Prior to assembly of the contact member 14 into theinsulator, the wire 20 should curl about but extend slightly outwardlyat its free end from the contact cap, as shown at 22 in Figure 4. Thewire may be of any suitable metal such as steel, so long as it hassutficient resilience to maintain the free end thereof under tensionagainst the insulator when the cap is in its assembled position withinthe threaded portion 18 of the centerbore, as shown in Figure 3.

In making the contact cap 14, the body member is formed with an upperthreaded portion, a lower threaded portion and an unthreaded centerportion having a height equal to that which would otherwise be occupiedby approximately one turn of the thread. If desired, a groove 24, fornesting of the wire 20, may be provided in the unthreaded portion. Thenone end of the wire 20 is welded adjacent the end of the thread on thelower portion and looped around so that its free end is adjacent thebeginning of the thread on the upper portion. It. is not essential toprecisely position the free end since, when the cap 14 is threaded intothe insulator, the wire will be guided by the threads of the insulatorinto its proper position to form a continuation of the thread formed onthe body of the cap 14. To assemble the various elements of thecenterwire, the electrode spindle 10 is first sealed into the centerboreas by means of a conductive glass seal of the type shown and claimed inUnited States Patent 2,248,415, issued to Karl Schwartzwalder andAlexander S. Rulka, after which the resistor cartridge 12 and spring 16are dropped into place. Then the hollow contact cap 14 is threaded intothe centerbore thereby applying tension against spring 16. A slot 26 isprovided in the top of the cap as a means for turning it into position.The shape and resiliency of the wire 20 allows the contact cap to bevery easily threaded into the insulator, the free end of the wire beingfree to flex inwardly and nest against the contact cap. But once in, thewire maintains the cap secured against removal, this by way of thebinding efiect of the free end of the wire against the ceramicinsulator. When attempt is made to unscrew the contact cap, the free endof the wire 20 flexes outwardly into binding engagement with therelatively rough surface of the ceramic. Thus, the entire assembly issecurly locked into place.

It will be understood that while the self-locking threaded element isparticularly advantageous in combination, as an electrical contact, inspark plugs and the like, it is contemplated that it may be used invarious other devices and structures. Also, it is contemplated thatvarious changes and modifications may be used, all within the full andintended scope of the claims which follow.

I claim:

1. A spark plug comprising a ceramic insulator having a centerbore witha threaded portion, a generally cylindrical hollow electrical contactmember having an open end and an external thread in engagement with thethreaded portion of said insulator, and a spiral spring extending intosaid hollow contact member through the open end thereof and biasedagainst said contact member, a portion of the thread on said contactmember being formed by a resilient metal wire having one end secured tosaid member and the other end in resilient engagement with saidinsulator to thereby securely lock said contact member within saidinsulator.

2. A spark plug comprising a ceramic insulator having a centerbore witha threaded portion of enlarged diameter at one end thereof, an electrodespindle sealed within said centerbore at the other end thereof, aresistor cartridge within said centerbore electrically connected to saidelectrode spindle, a generally cylindrical hollow electrical contactmember open at one end thereof and having an external thread inengagement with the threaded portion of said insulator, a center portionof approximately one References Cited in the file of this patent UNITEDSTATES PATENTS Daly July 9, 1918 Lovejoy Sept. 23, 1919 Minniurn Feb. 9,1937 Weatherly Feb. 8, 1949

